The invention concerns a transmission, in particular for motor vehicles, with an input shaft coupled with at least one power-splitting gear set that is capable of being coupled with an output shaft and with two electrical machines coupled with the at least one power-splitting ear set.
A transmission of this type was made known in U.S. Pat. No. 5,571,058. It has an input shaft that is coupled with power-splitting gear sets that are capable of being coupled with an output shaft. Each of the power-splitting gear sets is coupled with one of the electrical machines.
To enhance the overall efficiency levelxe2x80x94which is to be achieved during constant driving conditions in particularxe2x80x94four different driving conditions are possible. For this purpose, a clutch is provided for each driving condition, i.e., four clutches are required. Power flow always takes place through at least one of the six epicyclic gear sets in all. As a result, the design of this transmission is very complex. Weight and costs are increased as a result.
Moreover, a transmission is made known in U.S. Pat. No. 5,558,589 in which power flow always takes place through at least one epicyclic gear set. A plurality of clutches is provided in this case as well, which also results in increased costs.
In contrast, the transmission according to the invention, in particular for motor vehicles, has the advantage that is has a simpler design yet still features good efficiency levels. For this purpose, means are provided for coupling the input shaft with the output shaft while the electrical machines and the epicyclic gear sets are bridge. The means serve to couple the input shaft with the output shaft while the electrical machines are bridged and relative motions of the gear-set components of the epicyclic gear sets are suppressed.
Even when the electrical machine and the epicyclic gear set are bridged, the electrical machine can still work under load, i.e., in boost mode, to recuperate braking energy, and to operate as an alternator. The vehicle can still be operated with the full comfort of continuously-variable changes in conversion ratios even in the limp-home operating mode, i.e., if an electrical machine fails.
A positive connection of the input shaft with a transmission shaft prevents wear induced by friction couplings. The design is particularly simple when a pair of gear wheels is located between the input shaft and a transmission shaft.
Moreover, the use of two transmission shafts makes it possible to shift gears without disengaging the power transmission. The use of two electrical machines also makes it possible to obtain a continuously-variable conversion ratio in the range between two fixed ratios.